Hypochlorite ion is one of reactive oxygen species whose function in organisms has recently been focused. It is considered that bactericidal action of neutrophils is mainly derived from hypochlorite ion. Hypochlorite ion has been shown to be generated from hydrogen peroxide and chloride ions by myeloperoxidase in azurophilic granules in vitro (Klebanoff, S. J., and Clark, R. A. (1978) The Neutrophils: Function and Clinical Disorders, North-Holland Publishing Company, Amsterdam, Netherlands). In addition, hypochlorite ion is considered to play an important role in injury to the vascular endothelial surface in platelet-activating factor-induced microvascular damage (Suematsu, M., Kurose, I., Asako, H., Miura, S., and Tsuchiya, M. (1989) J. Biochem. 106, 355-360). However, it has been difficult to conclude that hypochlorite ion participates directly in the aforementioned mechanism in organisms, because a completely selective measuring method for hypochlorite ion, especially a measuring method in vivo had not been established.
Ten and several methods such as chemiluminescence, electron spin resonance (ESR), and luminescence are known as methods for measuring reactive oxygen species. Among them, the fluorescence detection method is superior from viewpoints of sensitivity and experimental convenience. In the fluorescence detection method, DCFH (2′,7′-dichlorodihydrofluorescein) or the like is used as a fluorescence probe for measuring reactive oxygen species. However, DCFH cannot successfully distinguish types of reactive oxygen species, and as a consequence, fails to selectively measure hypochlorite ion.